The present invention relates generally to compositions for preventing iron and acid induced sludge formation and emulsion formation during acidizing treatments of crude hydrocarbon wells.
A common practice to increase production from a crude oil or gas well involves an acid stimulation treatment of the well. Acid stimulation of a well involves the pumping downhole of an aqueous acid solution which reacts with the subterranean hydrocarbon containing formations, such formations usually consisting of limestone or sand, to increase the size of the pores within the formations and provide enlarged passageways for the crude hydrocarbons to more freely move to collection points which otherwise would be obstructed. Unfortunately, during such acidizing operations, asphaltene precipitates may form which block the existing and newly formed passageways and reduce the efficacy of the acidizing treatment. The formed asphaltic sludges vary in appearance depending on the types of acid additives used, the amount and state of iron present, and the nature of the crude.
In addition, crude hydrocarbons often contain chemicals that may stabilize an emulsion formed upon contact and mixing under shear conditions with the aqueous acid during an acid stimulation treatment. Emulsions so formed are often stable for many hours and present the possibility of forming emulsion blocks within the formation under bottom hole conditions. Such emulsions are undesirable because of the significant increase in the viscosity of the mixed crude and pumped fluids, with the result of impeded flow into and out from the well bore. Also, stable acid/crude emulsions are often formed from mixing the crude oil and spent acid.
Many additives and chemical compositions exist which are classified as anit-sludgerds, non-emulsifiers or demulsifiers, mutual solvents, iron controllers, or corrosion inhibitors. For example, U.S. Pat. No. 5,622,921 ('921 patent), which is incorporated by reference herein in its entirety, discloses the use of various additives that may be included in the acidizing solution to minimize sludge and emulsion formation in the hydrocarbon/acid solution. In particular, the '921 discloses a composition for controlling sludge and emulsion formation, the composition including a mixture of an anionic alkyl aryl sulfonic acid or sulfonate combined with nonethoxylated glycols and acetylenic alcohols in an alkyl alcohol solvent.
While known compositions are effective for reducing sludge and emulsion formation for some types of crude hydrocarbons and pumping conditions, they do not consistently perform well with the wide variety of crudes and conditions encountered in the field. In particular, known compositions do not resolve live acid and spent acid emulsions for some crude oils. “Live acid” refers to the acid solution at full strength; that is, as it is pumped into the formation (i.e. prior to reaction with carbonates, dolomite, limestone, etc.). “Spent acid” refers to solution after it has reacted with the well formation. For example, a live acid solution may be 15% hydrochloric acid, with the spent acid solution being 1% hydrochloric acid. It is important for emulsion control to prevent the formation of emulsions under both the live and spent conditions
While such currently used techniques and acidizing mixtures have achieved varying degrees of success, the current treatments have failed to produce consistently the necessary emulsion control for both live and spent acid conditions. It is, therefore, a purpose of the present invention to provide new and useful compositions for inhibiting or preventing the formation of emulsions in the presence of treating acids during the acid stimulation of hydrocarbon wells.